Automatic control system for ceiling fan based on temperature differentials

ABSTRACT

A fan includes a hub, several fan blades, and a motor that is operable to drive the hub. A motor controller is in communication with the motor, and is configured to select the rate of rotation at which the motor drives the hub. The fan is installed in a place having a floor and a ceiling. An upper temperature sensor is positioned near the ceiling. A lower temperature sensor is positioned near the floor. The temperature sensors communicate with the motor controller, which includes a processor configured to compare substantially contemporaneous temperature readings from the upper and lower temperature sensors. The motor controller is thus configured to automatically control the fan motor to minimize the differences between substantially contemporaneous temperature readings from the upper and lower temperature sensors. The fan system may thus substantially destratify air in an environment, to provide a substantially uniform temperature distribution within the environment.

PRIORITY

This application is a continuation of International Patent ApplicationSerial No. PCT/US2009/032935, entitled “Automatic Control System forCeiling Fan Based on Temperature Differentials,” filed Feb. 3, 2009,published as WO 2009/100052 on Aug. 13, 2009, the disclosure of which isincorporated by reference herein in its entirety, and which claimspriority from the disclosure of U.S. Provisional Patent Application Ser.No. 61/025,852, entitled “Automatic Control System for Ceiling Fan Basedon Temperature Differentials,” filed Feb. 4, 2008, the disclosure ofwhich is incorporated by reference herein in its entirety.

BACKGROUND

A variety of fan systems have been made and used over the years in avariety of contexts. For instance, various ceiling fans are disclosed inU.S. Pat. No. 7,284,960, entitled “Fan Blades,” issued Oct. 23, 2007,the disclosure of which is incorporated by reference herein; U.S. Pat.No. 6,244,821, entitled “Low Speed Cooling Fan,” issued Jun. 12, 2001,the disclosure of which is incorporated by reference herein; U.S. Pat.No. 6,939,108, entitled “Cooling Fan with Reinforced Blade,” issued Sep.6, 2005, the disclosure of which is incorporated by reference herein;U.S. Pub. No. 2008/0008596, entitled “Fan Blades,” published Jan. 10,2008, the disclosure of which is incorporated by reference herein; andU.S. Provisional Patent Application Ser. No. 61/034,254, entitled“Ceiling Fan System with Brushless Motor,” filed Mar. 6, 2008, thedisclosure of which is incorporated by reference herein. Alternatively,any other suitable fans may be used in conjunction with embodimentsdescribed herein.

The outer tip of a fan blade or airfoil may be finished by the additionof an aerodynamic tip or winglet. Merely exemplary winglets aredescribed in U.S. Pat. No. 7,252,478, entitled “Fan BladeModifications,” issued Aug. 7, 2007, the disclosure of which isincorporated by reference herein; U.S. Pub. No. 2008/0014090, entitled“Cuffed Fan Blade Modifications,” published Jan. 17, 2008, thedisclosure of which is incorporated by reference herein; and U.S. Pub.No. 2008/0213097, entitled “Angled Airfoil Extension for Fan Blade,”published Sep. 4, 2008, the disclosure of which is incorporated byreference herein. Other suitable structures that may be associated withan outer tip of an airfoil or fan blade will be apparent to those ofordinary skill in the art in view of the teachings herein.Alternatively, the outer tip of an airfoil or fan blade may be simplyclosed, or may lack any similar structure at all.

The interface of a fan blade and a fan hub may also be provided in avariety of ways. For instance, an interface component is described inU.S. Non-Provisional patent application Ser. No. 12/233,783, entitled“Aerodynamic Interface Component for Fan Blade,” filed Sep. 19, 2008,the disclosure of which is incorporated by reference herein.Alternatively, the interface of a fan blade and a fan hub may includeany other component or components, or may lack any similar structure atall.

Fans may also include a variety of mounting structures. For instance, afan mounting structure is disclosed in U.S. Non-Provisional patentapplication Ser. No. 12/203,960, entitled “Ceiling Fan with AngledMounting,” filed Sep. 4, 2008, the disclosure of which is incorporatedby reference herein. In addition, a fan may include sensors or otherfeatures that are used to control, at least in part, operation of a fansystem. For instance, such fan systems are disclosed in U.S.Non-Provisional patent application Ser. No. 12/249,086, entitled“Ceiling Fan with Concentric Stationary Tube and Power-Down Features,”filed Oct. 10, 2008, the disclosure of which is incorporated byreference herein; and U.S. Non-Provisional patent application Ser. No.12/336,090, entitled “Automatic Control System and Method to MinimizeOscillation in Ceiling Fans,” filed Dec. 16, 2008, the disclosure ofwhich is incorporated by reference herein. Alternatively, any othersuitable mounting structures and/or fan systems may be used inconjunction with embodiments described herein.

The effectiveness of very large, High Volume/Low Speed (“HVLS”) ceilingfans as a component of a climate control system in buildings may bereadily observed, such as in warm weather when the fans are either usedalone or in conjunction with air conditioning, and in winter when theyare used in conjunction with a heating system. In the absence of suchfans in some settings, natural convection may cause the air to stratify,with the warmest layers at the top adjacent to the roof and the coolestlayers at the floor. This may be a particularly undesirable condition inwinter, when occupants at floor level may desire heat, and hightemperatures just below the roof may increase the rate of thermal lossthrough the roof and decrease energy efficiency.

A primary function of an HVLS fan in such an environment, particularlyin winter months when the HVLS fan is used in conjunction with a heatingsystem, may be to maintain a substantially uniform air temperaturethroughout the enclosed space by blending the heated air from the upperpart of the space with the cooler air closer to the floor. A comfortableand energy-efficient condition may be maintained when the speed of thefan is controlled so that there is just enough air movement to maintainuniform air temperature without excessive speed that might createundesirable drafts. In practice, this condition may be only approximatedin many situations. For instance, the speed of the fan may be controlledeither manually (e.g., by a control operated by a person at floor level,etc.), or automatically (e.g., by coupling the fan to the controls ofthe heating system, etc.). In manual operation, the fan may becontrolled on the basis of the operator's subjective sense of comfort;and in heating-coupled automatic operation, it may be responsive to roomtemperature. However, such bases of control may not necessarily providea substantially uniform temperature throughout the space.

While a variety of systems and techniques have been made and used tocontrol fans and fan systems, it is believed that no one prior to theinventor has made or used the invention recited in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims which particularly pointout and distinctly claim the invention, it is believed the presentinvention will be better understood from the following description ofcertain examples taken in conjunction with the accompanying drawings, inwhich like reference numerals identify the same elements and in which:

FIG. 1 depicts a schematic view of an exemplary fan system includingcontrol components; and

FIG. 2 depicts a schematic view of control components of the fan systemof FIG. 1.

Reference will now be made in detail to various embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. To the extent that specific dimensions are shown in theaccompanying drawings, such dimensions should be regarded as merelyillustrative and not limiting in any way. Accordingly, it will beappreciated that such dimensions may be varied in any suitable way.

DETAILED DESCRIPTION

The following description of certain examples of the invention shouldnot be used to limit the scope of the present invention. Other examples,features, aspects, embodiments, and advantages of the invention willbecome apparent to those skilled in the art from the followingdescription, which is by way of illustration, one of the best modescontemplated for carrying out the invention. As will be realized, theinvention is capable of other different and obvious aspects, all withoutdeparting from the invention. Accordingly, the drawings and descriptionsshould be regarded as illustrative in nature and not restrictive.

As shown in FIG. 1, an exemplary fan (10) is coupled with a ceilingstructure (2), and is suspended over a floor (4). Fan (10) includes asupport (12), which is directly coupled with ceiling structure (2).Support (12) may be constructed and/or operable in accordance with theteachings of any of the patents, patent publications, or patentapplications cited herein. Fan (10) also includes a motor (14), a hub(16) that is rotated by motor (14), and a plurality of fan blades (18)extending radially outwardly from hub (16). Again, any of thesecomponents, among other components that fan (10) may have as desired,may be constructed and/or operable in accordance with the teachings ofany of the patents, patent publications, or patent applications citedherein.

A motor controller (20) is in communication with motor (14). Forinstance, motor controller (20) may include a programmable variablespeed control (24), providing a spectrum of speeds at which hub (16) maybe rotated by motor (14). Suitable components and features of motorcontroller (20) will be apparent to those of ordinary skill in the artin view of the teachings herein. Motor controller (20) may communicatewith motor (14) via wire (62), wirelessly, or in any other suitablefashion. A user interface (not shown) may also be in communication withmotor controller (20), permitting an operator to adjust speed settings(e.g., select from discrete pre-defined speeds or select a speed from asubstantially continuous range of speeds, etc.) for motor (14) throughmotor controller (20). By way of example only, a suitable user interfacemay comprise a wall-mounted control panel that is configured andoperable in accordance with the teachings of U.S. Provisional PatentApplication Ser. No. 61/034,254, entitled “Ceiling Fan System withBrushless Motor,” filed Mar. 6, 2008, the disclosure of which isincorporated by reference herein. Alternatively, any other suitable userinterface may be used. In the present example, the user interfacecommunicates with motor controller (20) via a wire (not shown). However,it should be understood that a user interface may alternativelycommunicate with motor controller (20) wirelessly or in any othersuitable fashion.

It should also be understood that motor controller (20) and a userinterface may be provided in any suitable location. By way of exampleonly, motor controller (20) may be located within or adjacent to motor(14). Alternatively, motor controller (20) may be located within oradjacent to a user interface, or somewhere else between a user interfaceand motor (14). Alternatively, motor controller (20) may be provided atany other suitable location. Similarly, a user interface may be mountedto a wall, may be provided by a computer that is far remote from thelocation in which fan (10) is installed, or may be provided at any othersuitable location.

As also shown in FIG. 1, the system of the present example furthercomprises two temperature sensors (40, 50) that are in communicationwith motor controller (20). Sensors (40, 50) may communicate with motorcontroller (20) via wires (64, 65), wirelessly, or in any other suitablefashion. Sensors (40, 50) may also communicate with an HVAC controlsystem, such that temperatures sensed by sensors (40, 50) may alsoaffect operation of a building's HVAC system in addition to or in lieuof affecting operation of fan (10). Motor controller (20) of thisexample includes a processor (22) that compares substantiallycontemporaneous temperature readings provided by the two sensors (40,50). Motor controller (20) then adjusts the speed at which hub rotates(16), based on the comparison of the substantially contemporaneoustemperature readings, as described in greater detail below. Of course,any suitable type of circuit or module may be used to control the speedof motor (14). Furthermore, processor (22) or other device that comparestemperature readings and/or issues associated commands may be integralwith or separate from a motor controller (20). Suitable rates forpolling temperature sensors (40, 50) (e.g., once every two seconds) willbe apparent to those of ordinary skill in the art in view of theteachings herein.

By placing one temperature sensor (40) nearer the ceiling (2) and asecond sensor (50) nearer the floor (4), the difference between the tworeadings may represent the degree to which operation of fan (10) isrequired to establish a desired uniform temperature condition. Forinstance, the system may be programmed such that a larger differencebetween the two temperature readings results in a progressively fasterspeed of fan (10); and the speed of fan (10) may be controlled toprogressively decrease as the difference between temperature readingsdecreases.

When the two temperature readings become approximately equal or within apredefined range of acceptable difference, fan (10) may reactaccordingly. For instance, when the two temperature readings becomeapproximately equal or within a predefined range of acceptabledifference, fan (10) may resume whatever speed it had before thedifference between the two temperature readings exceeded a predefinedthreshold. Alternatively, fan (10) may stop (e.g., power to the motor(14) ceases, such that fan (10) may “coast” to a stop; decelerate to astop in a controlled manner; or abrupt stop due to mechanical braking ormotor braking; etc.) when the two temperature readings becomeapproximately equal or within a predefined range of acceptabledifference; with fan (10) starting to rotate again as soon as the systemdetects the temperature difference exceeding a predefined threshold. Fan(10) may also be constantly running, with the speed of fan (10)constantly changing or often changing, dynamically responding to sensedtemperature differences as they are detected. Other ways in which a fan(10) may be controlled based on two or more temperature readings (e.g.,in response to the temperature differences exceeding a predefinedthreshold and/or in response to the sensed temperatures beingapproximately equal or within a predefined range of acceptabledifference) will be apparent to those of ordinary skill in the art inview of the teachings herein. Suitable ranges of difference between anupper temperature and a lower temperature for causing a fan (10) to stopor otherwise react will also be apparent to those of ordinary skill inthe art in view of the teachings herein.

After an upper temperature reading and lower temperature reading havebecome approximately equal or within a tolerable range (e.g., such thatthe room as sufficiently destratified), and fan (10) has stopped orotherwise reacted (e.g., merely slowed down, even if just slightly), thedifference between an upper temperature reading and a lower temperaturereading may still be monitored. For instance, temperature sensors (40,50) may be polled every few seconds or at any desirable rate while fan(10) is stopped or while fan (10) is operating at a user-defined speed.When the difference between the upper temperature and lower temperatureexceeds a threshold, processor (22) may send a signal to VFD (24) toagain initiate rotation of fan (10). To the extent that a fan (10) isdeactivated or otherwise stopped when the two temperature readingsbecome approximately equal or within a predefined range of acceptabledifference, a suitable temperature differential threshold forre-activating fan (10) will be apparent to those of ordinary skill inthe art in view of the teachings herein, and may based on the particularlocation of fan (10) and/or other considerations. The temperaturedifference may again be monitored as noted above while fan (10) isoperating, and fan (10) may be controlled accordingly.

As noted above, in some versions, fan (10) may be constantly rotating,with the speed being dynamically controlled (e.g., sped up, slowed down,etc.) based on differences between sensed temperatures. For instance,the control system may be configured such that no range of differencebetween the temperatures is acceptable, such that fan (10) is constantlyreacting to even small differences in temperatures. To the extent thatthe difference between temperatures is relatively small orimperceptible, the speed of fan (10) may be substantially constant(e.g., a speed associated with a user's input at a control device,stopped, etc.).

In some versions, an upper temperature sensor (40) may be incorporatedinto the assembly of fan (10) itself. In addition or in the alternative,an upper temperature sensor (40) may comprise a separate unit installednear the ceiling (2). Upper temperature sensors (40) may also beinstalled on a wall or other structure. Other suitable locations forinstalling one or more upper temperature sensors (40) will be apparentto those of ordinary skill in the art in view of the teachings herein.Furthermore, any suitable number of upper temperature sensors (40) maybe used. To the extent that more than one upper temperature sensor (40)is used, the readings from the plurality of upper temperature sensors(40) may be averaged together for comparison against a lower temperaturelevel. Alternatively, data from a plurality of upper temperature sensors(40) may be used in a variety of alternative ways, in comparison to oneor more temperature levels sensed by lower temperature sensor(s) (50) orotherwise.

In some versions, a lower temperature sensor (50) may be incorporatedinto a control panel associated with motor controller (20). In additionor in the alternative, a lower temperature sensor (50) may comprise aseparate unit to be installed near the floor (4). Lower temperaturesensors (50) may also be installed on a wall or other structure. Othersuitable locations for installing one or more lower temperature sensors(50) will be apparent to those of ordinary skill in the art in view ofthe teachings herein. In addition, as noted above with respect to uppertemperature sensors (40), any suitable number of lower temperaturesensors (50) may be used. To the extent that more than one lowertemperature sensor (50) is used, the readings from the plurality oflower temperature sensors (50) may be averaged together for comparisonagainst an upper temperature level. Alternatively, data from a pluralityof lower temperature sensors (50) may be used in a variety ofalternative ways, in comparison to one or more temperature levels sensedby upper temperature sensor (40) or otherwise.

In some versions, a single pair of temperature sensors (40, 50) is usedto control a single fan (10). In other versions, a single pair oftemperature sensors (40, 50) is used to control a group of several fans(10). Other ways in which any number of temperature sensors (40, 50) andany number of fans (10) may be correlated will be apparent to those ofordinary skill in the art in view of the teachings herein. Of course,while two temperature sensors (40, 50) are included in the presentexample, it should be understood that any suitable number of temperaturesensors may be used in any suitable locations.

FIG. 2 shows a schematic view of an exemplary control configuration. Asshown, motor controller (20) comprises a processor (22) a VFD (24).Processor (22) communicates with VFD (24), which in turn communicateswith fan (10). Temperature sensors (40, 50) and a relative humiditysensor (60) communicate with processor (22). In the present example,processor (22) makes corrections to the speed of fan (10) via a PIDcontroller (Proportional, Integral, Derivative). Alternatively, anyother suitable type of controller may be used. In the present example,temperature differentials are constantly monitored by processor (22),resulting in a command speed to fan (10). In some versions, the setvalue (SV) (e.g., target temperature difference between upper sensor(40) and lower sensor (50)) is always zero. This may represent aperfectly destratified space. Alternatively, any other suitable SV maybe used. The sensed temperature difference (ΔT) is used as a processvariable (PV), which is compared to the SV. The error between these twovariables is then handled by processor (22) and PI loop logic, resultingin an adjusted fan command speed (MV, or manipulated variable).

To the extent that humidity sensor (60) is included, humidity sensor(60) may be placed at any suitable location. Furthermore, humidity dataobtained by humidity sensor (60) may be factored into a controlalgorithm in any suitable fashion, such as is described below orotherwise. Suitable ways in which humidity data may be used to influencecontrol of fan (10), such as in conjunction with data from temperaturesensors (40, 50), will be apparent to those of ordinary skill in the artin view of the teachings herein.

It should be understood that behavior of fan (10) may be varied based ona variety of factors, in addition to or in lieu of ΔT. For instance, thebehavior of fan (10) may be varied based on relative humidity (RH), thedifference between an indoor temperature and indoor temperature, and/orthe status of an HVAC system (e.g., whether an HVAC system is in aheating mode or cooling mode, etc.), among other possible factors orparameters. Furthermore, behavior of fan (10) might be different basedon whether the temperature is cooler outdoors than it is indoors, orwarmer outdoors than it is indoors (e.g., seasonal modes). Yet anothervariable that may control system response may include absolute roomtemperature (e.g., warm or cool, etc). Still other constants, variables,or parameters that may be used to influence behavior of fan (10) will beapparent to those of ordinary skill in the art in view of the teachingsherein.

In the present example, the speed of system response to error iscontrolled by proportional gain (Kp). In some versions, Kp is a numberthat may be derived from the following two places: relative humidity andVFD (24) acceleration/deceleration rates. Alternatively, Kp may bederived from only one of those factors, derived from any otherfactor(s), or derived from any suitable combination of factors. In thepresent example, Kp(RH) defines the level of aggression by which the fan(10) will respond to error, such as will be described in greater detailbelow or otherwise.

A system may also provide a “Summer mode,” “Winter mode” and/or avariety of other modes. Such modes may be selected manually orautomatically (e.g., based on an electronic timer or calendar, based onoutdoor temperatures, temperature trends, other environmentalconditions, etc.). By way of example only, in a Summer mode, highervalues of RH may result in a higher Kp. In a Winter mode, higher valuesof RH may result in a lower Kp. Further exemplary details of Wintermodes and Summer modes will be described in greater detail below. Ofcourse, any other suitable modes may be used, and may have any suitableeffect on Kp. Furthermore, any other suitable control configuration,components, parameters, and functions may be used.

The following TABLE 1 shows various exemplary ranges of parameters underwhich various versions of fan (10) may be operated. It will beappreciated, however, that the numerical values and ranges shown in thetable are merely exemplary and are merely approximate. They are notintended to be exhaustive, definitive, or limiting in any way. Instead,they merely represent several of numerous possible ways in which a fansystem may be operated.

TABLE 1 Processor “Interpreted” “Real World” Values Values ProcessorAnalog 0.0~10.0 VDC 2~1018 10 Bit Resolution Output Span ProcessorAnalog 0.0~10.0 VDC 2~1018 10 Bit Resolution Input Span TemperatureSensor 5°~140° 103~513 10 Bit Resolution Outputs Fahrenheit 3.037 Bits/°F. 1.0~5.0 VDC Humidity Sensor 5%~95% RH 123~493 10 Bit ResolutionOutputs 1.2~4.8 VDC 4.11 Bits/% RH Range Low 50°~75° 240~316 10 BitResolution Fahrenheit Range High 85°~105° 346~407 10 Bit ResolutionFahrenheit VFD Frequency 25~45 Hz 307~713 10 Bit Resolution 3.0~7.0 VDC20.32 Bits/Hz Analog Out

In the above TABLE 1, “Range Low” describes a break point between Winterand Summer automatic modes. For instance, when the temperature sensed bylower sensor (50) is below the 50° F. to 75° F. range, motor controller(20) will be automatically placed in Winter mode. In Winter mode, motorcontroller (20) may be configured to automatically performdestratification routines as described herein (e.g., control motor (14)based on differences between temperatures sensed by temperature sensors(40, 50) in order to reduce or eliminate such differences). When thetemperature sensed by lower sensor (50) within or above the 50° F. to75° F. range, motor controller (20) will be automatically placed inSummer mode. Of course, motor controller (20) may permit an installer oruser to adjust the “Range Low” range. Furthermore, “Range Low” may beomitted altogether, if desired (e.g., when there is no Winter/Summermode distinction).

Also in TABLE 1, “Range High” describes the temperature point at whichfan (10) may operate at 100% output (e.g., 60 Hz). The temperature spanbetween “Range Low” and “Range High” may be scaled to equal a fan outputbetween a VFD Frequency set point and full speed (e.g., 60 Hz). Again,motor controller (20) may permit an installer or user to adjust the“Range High” range; and “Range High” may be omitted if desired.

Also in TABLE 1, “VFD Frequency” describes the maximum speed of fan (10)in Winter mode, and the minimum speed of fan (10) in Summer mode. Forinstance, in Winter mode, fan (10) may be limited to speeds between 10Hz and 25 Hz to 45 Hz. In Summer mode, fan (10) may be limited to speedsbetween 25 Hz to 45 Hz and 60 Hz. Again, motor controller (20) maypermit an installer to adjust the “VFD Frequency” range.

In some versions, and as referred to above, motor controller (20) mayprovide three different modes—Winter mode, Summer mode, and Manual mode.In an example of Winter mode, the system may act as an automaticdestratification controller. Floor temperature, as sensed by lowertemperature sensor (50), may be subtracted from ceiling temperature, assensed by upper temperature sensor (40), to define ΔT of the space. Thisvalue may then be scaled against a user-defined low speed range todetermine an optimum rate of rotation for fan (10). The user may definethis range by adjusting the “VFD Frequency” parametric setting. Forinstance, if the setting is 30 Hz, then the Winter speed range may bebetween 10 Hz and 30 Hz. The system may constantly fine tune therotational speed of fan (10) in order to achieve a ΔT that is equal toor at least close to zero, which should reflect a substantiallydestratified space. In an effort to address “wind chill” effects, thesystem may monitor relative humidity in the space, such as with relativehumidity sensor (60). When humidity is higher than 60% (or any othersuitable threshold), the system may scale back the response time of thespeed change of fan (10) based on internal algorithms. Longer responsetimes may allow the room to destratify without creating air velocitiesthat could potentially become comfortable in colder temperatures.

In an example of Summer mode, the system may run fan (10) at a speedrelative to the temperature span between “Range Low” and “Range High,”as defined by the user. This predefined temperature range may be scaledagainst a user defined high speed range to determine an optimumrotational rate for fan (10). The user may define the speed range byadjusting the “VFD Frequency” setting. For instance, if the VFDFrequency setting is 35 Hz, then the summer speed range may be between35 Hz and 60 Hz. Of course, any other suitable ranges may be used.

In an example of Manual mode, the system runs fan (10) at a speed asdefined by the user through any suitable user input device. Such a speedmay be unaffected by temperatures sensed by temperature sensors (40,50). Of course, the above described Winter, Summer, and Manual modes aremerely exemplary. Such modes may be modified or omitted as desired, andany other suitable mode(s) may be provided.

In some versions, other properties of fan (10) may be controlled basedon temperature differentials or other factors, in addition or in lieu ofcontrolling the rate of rotation of fan. By way of example only, theangle of attack at which blades (18) are mounted to hub (16) or bladepitch may be adjusted to affect fan performance, based on temperaturedifferentials or other factors. The angle of attack or blade pitch maybe adjusted using servos, louver actuators, hydraulics, pneumatics, orany other suitable components, devices, mechanisms, or techniques. Stillother ways in which temperature differentials and/or other environmentalconditions may be used to affect performance of a fan (10), includingbut not limited to physical properties of fan (10) and/or operation offan (10), will be apparent to those of ordinary skill in the art in viewof the teachings herein.

Having shown and described various embodiments of the present invention,further adaptations of the methods and systems described herein may beaccomplished by appropriate modifications by one of ordinary skill inthe art without departing from the scope of the present invention.Several of such potential modifications have been mentioned, and otherswill be apparent to those skilled in the art. For instance, theexamples, embodiments, geometrics, materials, dimensions, ratios, steps,and the like discussed above are illustrative and are not required.Accordingly, the scope of the present invention should be considered interms of the following claims and is understood not to be limited to thedetails of structure and operation shown and described in thespecification and drawings.

1-20. (canceled)
 21. A fan system installed in a location having a floorand a ceiling, the fan system comprising: a rotatable hub; a pluralityof fan blades secured to the hub; a motor in communication with the hub,wherein the motor is operable to drive the hub at a selectable rate ofrotation; a motor controller in communication with the motor, whereinthe motor controller is configured to select the rate of rotation atwhich the motor drives the hub; an upper temperature sensor positionednear the ceiling, wherein the upper temperature sensor is configured tosense the temperature of air near the ceiling, wherein the uppertemperature sensor is in communication with the motor controller; and alower temperature sensor positioned near the floor, wherein the lowertemperature sensor is configured to sense the temperature of air nearthe floor, wherein the lower temperature sensor is in communication withthe motor controller; wherein the motor controller is configured toautomatically adjust the rate of rotation at which the motor drives thehub from a first non-zero rate of rotation to a second non-zero ofrotation based at least in part on differences between temperaturescommunicated from the upper temperature sensor and temperaturescommunicated from the lower temperature sensor.
 22. The fan system ofclaim 21, wherein the motor controller is configured to comparetemperatures communicated from the upper temperature sensor totemperatures communicated from the lower temperature sensor.
 23. The fansystem of claim 22, wherein the motor controller is configured toautomatically adjust the rate of rotation at which the or drives the hubto minimize differences between temperatures communicated from the uppertemperature sensor and temperatures communicated from the lowertemperature sensor.
 24. The fan system of claim 21, wherein the motorcontroller comprises a processor and a variable frequency drive.
 25. Thefan system of claim 24, wherein the upper temperature sensor and thelower temperature sensor are coupled with the processor, wherein theprocessor is coupled with the variable frequency drive, wherein thevariable frequency drive is coupled with the motor.
 26. The fan systemof claim 24, wherein the processor comprises a Proportional, Integral,Derivative (PID) controller.
 27. The fans systems of claim 26, whereinthe PID is associated with a set value (SV) of zero.
 28. The fan systemof claim 27, wherein the PID is further associated with a processvariable (PV), wherein the process variable represents the differencebetween a temperature sensed by the upper temperature sensor and atemperature substantially contemporaneously sensed by the lowertemperature sensor.
 29. The fan system of claim 28, wherein the PID isconfigured to process errors between the SV and PV values through a PIloop logic.
 30. The fan system of claim 21, wherein the motor controlleris configured to provide a first mode of operation and a second mode ofoperation, wherein the first mode of operation includes a first upperlimit on the rate of rotation at which the motor drives the hub, whereinthe second mode of operation includes a second upper limit on the rateof rotation at which the motor drives the hub, wherein the second upperlimit is higher than the first upper limit.
 31. The fan system of claim30, wherein the first mode of operation further includes a first lowerlimit on the rate of rotation at which the motor drives the hub, whereinthe second mode of operation further includes a second lower limit onthe rate of rotation at which the motor drives the hub, wherein thesecond lower limit is higher than the first lower limit.
 32. A method ofoperating a fan comprising the steps of: providing a fan in a locationhaving a floor and a ceiling, said fan comprising: a rotatable hub; aplurality of fan blades secured to the hub; a motor in communicationwith the hub, wherein the motor is operable to drive the hub at aselectable rate of rotation; and a motor controller in communicationwith the motor, wherein the motor controller is configured to select therate of rotation at which the motor drives the hub; providing an uppertemperature sensor for sensing a temperature near the ceiling and alower temperature sensor for sensing a temperature near the floor;receiving an upper temperature reading from the upper temperature sensorand a lower temperature reading from the lower sensor; and adjusting therate of rotation at which the motor drives the hub from a first non-zerorate of rotation to a second non-zero rate of rotation based at least inpart on differences between the upper and the lower temperatures. 33.The method of claim 32, further including the step of: automaticallyplacing the motor controller in one of a first mode or second mode,wherein the motor controller is placed in the first mode when the lowertemperature is below a first temperature, and wherein the motorcontroller is placed in the second mode when the lower temperature isabove the first temperature; and wherein the adjusting step comprisesadjusting the rate or rotation to a first speed in the first mode and asecond speed in the second mode, wherein the first speed is slower thanthe second speed.
 34. The method of claim 33, wherein the adjusting stepfurther includes automatically adjusting the rate of rotation tominimize differences between subsequent temperature readings from theupper and lower temperature sensors.
 35. The method of claim 34, furthercomprising the steps of: continuously receiving temperature readingsfrom the upper temperature sensor; continuously receiving temperaturereadings from the lower temperature sensor; and continuously adjustingthe rate of rotation at which the motor drives the hub based at least inpart on differences between the continuously received temperaturereadings from the upper and lower temperature sensors.
 36. The method ofclaim 32, further comprising the steps of: providing a humidity sensorfor sensing a relative humidity; receiving a relative humidity readingfrom the humidity sensor; and adjusting the rate of rotation at whichthe motor drives the hub based further at least in part on the humidityreading.